Andreev O, Borejdo J
Baylor Research Institute, Baylor University Medical Center, Dallas, TX 75226.
Biochem Biophys Res Commun. 1992 Oct 15;188(1):94-101. doi: 10.1016/0006-291x(92)92354-z.
During a part of the hydrolytic cycle, myosin head (S1) carries no nucleotide and binds strongly to an actin filament forming a rigor bond. At saturating concentration of S1 in rigor, S1 is well known to form 1:1 complex with actin. However, we have provided evidence that under certain conditions S1 could also form a complex with 2 actin monomers in a filament (Andreev, O.A. & Borejdo, J. (1991) Biochem. Biophys. Res. Comm. 177, 350-356). This view was recently challenged by Carlier & Didry (Carlier, M-F. & Didry, D. (1992) Biochem. Biophys. Res. Comm. 183, 970-974) who interpreted our data by suggesting that F-actin underwent a simple depolymerization and implied that, when only actin in the F-form was scored, the real stoichiometry in our experiments was 1:1. We show here that under conditions of our experiments less than 8% of actin was depolymerized. Moreover, we have repeated the experiments in the presence of phalloidin and show that under these conditions too, when S1 was added slowly to a fixed concentration of F-actin, it formed a different complex with F-actin than when it was added quickly. This confirms our original conclusion that S1 can bind actin in two different ways and shows that depolymerization of F-actin is not responsible for this finding.
在水解循环的某个阶段，肌球蛋白头部（S1）不携带核苷酸，并与肌动蛋白丝紧密结合形成强直键。在强直状态下S1达到饱和浓度时，众所周知S1会与肌动蛋白形成1:1复合物。然而，我们已经提供证据表明，在某些条件下S1也能与肌动蛋白丝中的两个肌动蛋白单体形成复合物（安德烈耶夫，O.A. & 博雷伊多，J.（1991年）《生物化学与生物物理研究通讯》177，350 - 356）。最近，卡利耶 & 迪德里（卡利耶，M - F. & 迪德里，D.（1992年）《生物化学与生物物理研究通讯》183，970 - 974）对这一观点提出了质疑，他们对我们的数据进行解释时认为F - 肌动蛋白发生了简单的解聚，并暗示当只对F型肌动蛋白进行计数时，我们实验中的实际化学计量比为1:1。我们在此表明，在我们的实验条件下，解聚的肌动蛋白不到8%。此外，我们在鬼笔环肽存在的情况下重复了实验，结果表明在这些条件下，当将S1缓慢添加到固定浓度的F - 肌动蛋白中时，它与F - 肌动蛋白形成的复合物与快速添加时不同。这证实了我们最初的结论，即S1可以通过两种不同方式结合肌动蛋白，并且表明F - 肌动蛋白的解聚与这一发现无关。
